The goals of this study will be to investigate the synaptic properties of the thalamocortical projection in the somatosensory and auditory pathways. The theoretical impetus motivating these studies is to understand the role of higher order thalamic relays in sensory processing, in particular as a potential link for interareal cortical communication, via a cortico-thalamo-cortical pathway. This study has relevance for understanding the normal, healthy modes of sensory processing in humans. The study will utilize in vitro slice preparations in the mouse, which have been developed for both the somatosensory and auditory systems. This will allow a comparison between multiple systems to test the generality of the observations. Intracellular recordings will be made from cortical neurons in layers IV and VI in first order (FO) and higher order (HO) cortical areas in the somatosensory and auditory systems. Minimal electrical stimulation and photostimulation by uncaging of glutamate will be used to activate neurons in FO and HO thalamic relays. Morphological correlates will be sought using intracellular injections of biocytin. The study should thus broaden our knowledge and perspective of the normal modes of sensory processing, and provide a foundation for the further exploration of abnormal sensory processing in neurological diseases.